A mobile communication system refers to a system in which an operator provides communication services for a user terminal (such as a mobile phone) by deploying a radio access network device (such as a base station) and a core network device (such as a Home Location Register, HLR). The mobile communication system has experienced the first generation, the second generation, the third generation, and the fourth generation. The first generation of the mobile communication system refers to the original analog, voice-only cellular phone standard, which mainly using an access method of analog technology and Frequency Division Multiple Access (FDMA). The second generation of the mobile communication system introduces digital technology, which improves network capacity and improves voice quality and confidentiality. Representative of the second generation of the mobile communication system is Global System for Mobile Communication (GSM) and Code Division Multiple Access (CDMA IS-95). The third generation of the mobile communication system mainly refers to three technologies including CDMA2000, WCDMA, and TD-SCDMA, which all use code division multiple access as access technology. Standards of the fourth generation of the mobile communication system are internationally uniform, which are Long Term Evolution/Long Term Evolution-Advanced (LTE/LTE-A) developed by the International Organization for Standardization (3GPP), whose downlink is based on Orthogonal Frequency Division Multiple Access (OFDMA) and uplink is based on Single Carrier-Frequency Division Multiple Access (SC-FDMA), which achieves high-speed transmission with a downlink peak rate reaches 1 Gbps and an uplink peak rate reaches 500 Mbps based on a flexible bandwidth and an adaptive modulation and coding scheme.
Based on the LTE R13 LAA downlink transmission method, the MulteFire standard defines the uplink transmission method, and may independently work in an unlicensed frequency band through technical enhancement.
Since the MulteFire standard works in the unlicensed bands, Listen-Before-Talk (LBT) technology which is similar to WiFi is introduced to ensure coexistence of the MulteFire standard with other technologies for unlicensed bands (such as WiFi). In order to ensure that a Discovery Reference Signal (DRS) for synchronization has sufficient transmission opportunities under the condition of LBT, the MulteFire standard defines a Discovery Measurement Timing Configuration (DMTC). The DMTC is a periodic window in which a cell attempts to transmit the DRS. Specifically, a minimum transmission cycle of the DMTC is 40 ms, and the length of the transmission window is 1-10 ms, which is configured by the cell.
In order to enable the MulteFire standard to independently work in the unlicensed band, physical layer technologies are enhanced as follows.
I. Synchronization Signal
The synchronization signal mainly includes Primary Synchronization Signals (PSS), Secondary Synchronization Signals (SSS), enhanced Primary Synchronization Signals (ePSS), and enhanced Secondary Synchronization Signals (eSSS). The synchronization signal may be part of the DRS, that is, transmitted within the DMTC. When the synchronization signal is transmitted on subframes 0 to 4, a short code of the SSS is 0. When the synchronization signal is transmitted on subframes 5 to 9, the short code of the SSS is 1. The synchronization signal may also be transmitted on subframes 0 or 5 that are outside the DMTC. In each subframe, the PSS is transmitted on the 7th OFDM symbol, the SSS is transmitted on the 6th OFDM symbol, the ePSS is transmitted on the 4th OFDM symbol, and the eSSS is transmitted on the 3rd OFDM symbol. With the enhanced design, the synchronization signal may enable a user terminal to obtain time and frequency synchronization information by once demodulation at a lower signal to noise ratio. Specifically, a boundary position of the subframe may be obtained, but a subframe number and a system frame number may not be obtained.
II. Enhanced Physical Broadcast Channel
The MulteFire Physical Broadcast Channel (MF-PBCH) mainly broadcasts a Master Information Block (MIB). The MF-PBCH may be part of the DRS and may be sent in any subframe within the DMTC. Three bits in the MIB indicate a subframe offset relative to subframe 0 or subframe 5. The user terminal may obtain the subframe number by demodulating information of the 3 bits. The MF-PBCH may also be transmitted on subframe 0 other than the DMTC.
In addition, similar to the LTE system, the MIB also indicates 8-bit system frame number information. Other 2-bit information is obtained through a redundant RV version of the MF-PBCH. The user terminal may obtain the system frame number (SFN) by blindly demodulating the RV version of the MF-PBCH and the 8-bit information broadcasted in the MIB, and complete all synchronization operations. For the reliability at the time of demodulation, the MF-PBCH occupies a total of 6 OFDM symbols of 7, 8, 9, 10, 11, and 4 for transmission.
III. Enhance System Information Block (eSIB)
The enhanced system information block (eSIB) may be part of the DRS and may be sent in any subframe within the DMTC. Unlike other DRS which occupy dedicated pilot resources, the eSIB occupies PDSCH resources. The eSIB may also be transmitted on subframe 0 other than the DMTC.
In the unlicensed frequency band, the CRS and the MF-PBCH may be sent within the DMTC or outside the DMTC. Therefore, the transmission opportunity is more and flexible. As such, the user terminal usually encounters following scenarios when demodulating the CRS and the MF-PBCH:
Scenario 1: when the DRS is transmitted within the DMTC and if the DRS is transmitted on subframes 0˜4, the CRS is scrambled with subframe 0. If the DRS is transmitted on subframes 5˜9, the CRS is scrambled with subframe 5. The user terminal may obtain a channel estimation result of the system by demodulating the CRS, and then demodulate the result to obtain the MulteFire physical broadcast channel (MF-PBCH), the physical downlink control channel (PDCCH), and the corresponding physical downlink shared Channel (PDSCH). When unicast data is transmitted within the DMTC, the CRS is scrambled according to a subframe number transmitting the CRS. Since the user terminal does not know whether the DRS or the unicast data is transmitted within the DMTC, the user terminal needs to blindly demodulate the CRS using various scrambling assumptions, which greatly improves the complexity of the demodulation and increases power consumption.
Scenario 2: in the MulteFire standard, the MF-PBCH may be sent on any subframe within the DMTC or on subframe 0 that is outside the DMTC. There are four RV versions transmitted by the MF-PBCH: RV0, RV1, RV2, and RV3. When a cell transmits the MF-PBCH, a RV version of the MF-PBCH transmitted at the moment of SFN mod 4=x is RVx. However, before demodulating the MF-PBCH, the user terminal does not know whether this moment is within the DMTC, and does not know a corresponding SFN value. Therefore, as shown in FIG. 5A, the user terminal needs to blindly demodulate the MF-PBCH according to all RV versions at all moments, which improves the complexity of the demodulation and increases the power consumption.
That is to say, when demodulating the CRS and the MF-PBCH currently, various assumptions are required for demodulation, resulting in high demodulation complexity and increased power consumption.